[Sanitizer] Introduce "stack_trace_format" runtime flag.

This flag can be used to specify the format of stack frames - user
can now provide a string with placeholders, which should be printed
for each stack frame with placeholders replaced with actual data.
For example "%p" will be replaced by PC, "%s" will be replaced by
the source file name etc.

"DEFAULT" value enforces default stack trace format currently used in
all the sanitizers except TSan.

This change also implements __sanitizer_print_stack_trace interface
function in TSan.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@221469 91177308-0d34-0410-b5e6-96231b3b80d8